1. Field of the Invention
This invention relates to a heat-generating element suitable for application in, for example, a microswitch (relay), sensor, or other small-size devices in particular, as well as to a manufacturing method and so on for the same.
2. Description of the Related Art
Conventionally, electrical components (devices) called switches have been used which perform electrical opening and closing of circuits. Such switches have been reduced in size as electronic technology has advanced in order to enable incorporation in electronic components such as measurement device, and have been provided, for example, as devices called microswitches (also known as microrelays).
A microswitch performs, for example, mechanical opening and closing between solid electrodes by means of a conductive liquid metal, or performs electrode switching operations to open and close electrical contacts and effect electrical connections. In a microswitch, a plurality of electrodes (here, the case of two electrodes is explained) are formed so as to be exposed at prescribed locations on the inner walls of a long thin channel sealed with a material having electrically insulating properties. On top of this, a member having electrically conducting properties (for example, a liquid metal of gallium, a gallium alloy, mercury, or similar) is injected into the channel to form a liquid column. The length of the liquid column is equal to or greater than the distance between at least two of the electrodes. When two electrodes are to be electrically connected (switch closed), the liquid column is caused to be in contact with the two electrodes simultaneously. When two electrodes are not to be electrically connected (switch opened), the liquid column is kept from being in contact with the two electrodes simultaneously (either the liquid column is prevented from making contact with the two electrodes, or is brought into contact with only one of the electrodes).
In Japanese Patent Laid-open No. 47-21645 and Japanese Patent Laid-open No. 9-161640, a microswitch is disclosed which performs operations to open and close electrical contacts by mechanically opening and closing the space between solid electrodes using a conductive liquid.
The microswitch is provided with a substrate having a heat-generating element or member equivalent thereto which, in order to cause this liquid column to move, heats the air (or, a gas, liquid or similar which is insulating or has low conductivity) within the channel to cause expansion, such that a pressure difference arises at the two ends of the liquid column. Conventionally, a heat-generating element used in such a microswitch or similar is formed by patterning of a metal film deposited onto a substrate.
Consequently adhesion with the substrate easily becomes unstable, and there are concerns that the reliability of the switching operation may become unstable. Also, when using mercury as the conductive member, the metal film which is the heater material and mercury vapor may form an amalgam (alloy with mercury), so that the heater characteristics change. Normally in such cases a protective film is formed with an Si3N4, SiO2, and the like on the heat-generating element surface in order to prevent amalgam formation; the process to form this protective film could be an extra necessary inconvenience. Also, problems with the drape properties of the protective film may result in degraded reliability. Moreover, heating efficiency may decline due to the thermal capacity of the protective film itself.
Hence an object of this invention is to obtain a heat-generating element and substrate which resolve such problems, and a method for manufacturing the same efficiently and highly accurately, as well as equipment using the same.